Modem ink jet printheads can consist of a plurality of nozzle holes, each fed by a series of passageways leading back to a larger ink reservoir. Collectively these features are described as flow features. Ink is ejected from the printhead through the nozzle holes by mechanical, thermal or other means allowing the device to form an image on a suitable media.
Because of the increasing demand for higher resolution printing, the size of these nozzle holes and flow features are being shrunk to ever smaller dimensions, permitting a smaller drop size, and hence a finer resolution image. Because of the increasing demand for greater speed when printing, the number of nozzle holes is being greatly increased on some devices. All of these progressive changes have led to an increasing sensitivity to clogging either in the nozzle or in the flow features leading to the nozzle.
Foreign debris commonly found in the manufacturing environment, particularly cellulose fibers and skin dander, are among the most common objects contaminating printheads during manufacture that will result in a nozzle clog. These debris are often larger than the dimensions of the flow features and occlude them, thereby preventing ink from feeding the firing chamber of the printhead and causing a print failure.
To minimize this from happening current manufacturing processes require the assembly of sensitive components in a cleanroom environment where particulate counts are strictly controlled. Even in these environments, however, some level of contamination still occurs. Since humans may necessarily be in the cleanroom, significant amounts of skin dander can be found in inks in printing devices processed in such cleanrooms. Similarly, paper products are so ubiquitous that significant amounts of cellulose can be found in inks in printing devices processed in cleanrooms.
Previous techniques attempt to limit the damage large particulates can cause in a printhead by filtering out the particle before it can completely occlude the nozzle or flow feature. Two common strategies are employed. One involves filtering the ink as it is drawn into the printhead from the reservoir. While effective, this will not eliminate particles pre-existing in the printhead itself from its construction.
The second strategy involves placing filter pillars before the passageway feeding the nozzle-firing chamber. The filter pillar effectively creates two paths to the firing chamber, such that if one becomes blocked, the other is still available.